1. Field of the Invention
The present invention relates to an organic electroluminescence device whose luminous region is substantially rectangular.
2. Description of the Related Art
Electrodes of an organic electroluminescence device have various restrictions such as a restriction that at least one electrode must have optical transparency, and a restriction that electrodes must be constituted by a material and production method which do not deteriorate an organic layer, and the like. Therefore, the material adoptable as electrodes of an organic electroluminescence device is limited extremely.
In addition, since an apparatus (for example, personal digital assistant etc.) equipped with an organic electroluminescence device has a limit in its size, the size of the device concerned also has restrictions. In consequence, the size and located positions of terminal sections of electrodes are also limited.
As a result, in plenty of respective current paths in which currents in the organic electroluminescence device flow, those resistances may largely differ. For this reason, for example, tho following problems have occurred.    Occurrence of Brightness Unevenness
Since locations where rich currents flow and locations where poor currents flow exist, brightness unevenness occurs as the entire device. This is because, since the luminance of the organic electroluminescence device becomes high as a flowing current becomes large, the difference of luminance occurs between both to become brightness unevenness, when a location where a rich current flows and a location where a poor current flows exist.    Occurrence of Lifetime Difference in Device
The lifetimes in a device differ in a location through which a rich current flows, and a location through which a poor current flows. Generally, a lifetime of a portion through which a rich current flows becomes short. For this reason, a location, which has a short lifetime in comparison with a device where a uniform current flows, exists, and hence, a lifetime as the organic electroluminescence device becomes short. In addition, when an organic electroluminescence device is used for a long time, a location not shining arises or a location whose luminance is lower than that of other locations arises.    Problems Such as Deterioration
Since a location through which a rich current flows and a location through which a poor current flows exist, a location being deteriorated may arise.    Occurrence of Chromaticity Unevenness
Since there are a location through which a rich current flows and a location through which a poor current flows, in a device, an S-S annihilation phenomenon arises in the case of an organic electroluminescence device using a fluorescent material, or a T-T annihilation phenomenon arises in the case of an organic electroluminescence device using a phosphorescence material, hence, in an organic, electroluminescence device which contains a plurality of luminescent materials in its luminescent layer, and in which each luminescent material emits a color with a wavelength different from at least one other luminescent material, it may arise that the luminance of each layer differs from others at a location where a current is easy to flow and a location where a current is hard to flow. As a result, the chromaticity unevenness may arise.
As for these problems, their advantages could be made small if, for example, it were possible to produce an organic electroluminescence device only with materials having small volume resistivity values, or a terminal section over the entire circumference of the device could be provided. But, since there are various restrictions as described above, they have actually arisen.
Hereinafter, resistance difference between respective paths, in which currents flow, in an organic electroluminescence device will be explained in detail by using FIG. 26.
In the organic electroluminescence device used for explanation here, an electrode provided in an optical output side rather than an organic layer is an anode formed of ITO, and a cathode, which faces the anode, is formed of aluminum, in this structure, since the volume resistivity or aluminum is very small in comparison with that of ITO, its volume resistivity can be disregarded substantially. Hence, only the anode which poses a problem (which is an electrode with high volume resistivity) at the time of considering the resistance difference between respective paths is shown in FIG. 26.
An anode 100 includes a terminal, section 110 to which an external drive circuit is connected, and a region (electrode region) 130, which contacts an organic layer. A region adjacent to the electrode region 130 in the organic layer becomes a region (luminous region) which a current is flowed in and emits light.
In order to eliminate problems such as brightness unevenness in the luminous region of the organic electroluminescence device with this structure, resistances from a point P0, at which the terminal section 110 contacts to the electrode region 130, on an electrode region 130 to respective points on the electrode region 130, for example, P1 to P2 must be equal.
Nevertheless, the volume resistivity of ITO is not such a small value that it can be ignored when the resistances of respective current paths in the organic electroluminescence device is considered. Hence, a resistance is small in a path, in which the distance of passing through ITO is short, such as the current path between P0 and P1, P2, or P3, and a resistance becomes large in a path, in which the distance of passing through ITO is long, such as the current path between P0 and P4, P5, or P6. Hence, the magnitude of a current which flows through the organic layer differs by a path, that is, a position in the luminous region, and as a result, brightness unevenness and the like arise.
FIG. 27 shows an organic electroluminescence device in which an anode a cathode are formed of ITO. In this figure, a continuous line shows the anode, and a doted line shows the cathode. A cathode 300 includes a terminal section 310 to which an external drive circuit is connected, and a region (electrode region) 330, which connects an organic layer.
In this organic electroluminescence device, since both electrodes are formed of ITO, both of the resistivity of the anode and the resistivity of the cathode cannot be ignored when the resistance difference between the above-mentioned respective paths is considered.
In this structure, the resistance of the path of passing through a path (minimum distance) L1 connecting the terminal sections 110 and 310 with a straight line becomes the smallest. Hence, the current, which flows in the organic layer on the path L1, becomes the largest and the current, which flows in the organic layer, becomes small as a path is apart from the path L1. As a result, brightness unevenness and the like arise.
Various types of prior art are proposed as prior art, which cancels brightness unevenness. For example, an electroluminescence device is also proposed, the device which includes a luminescent layer which is provided between first and second electrodes, and has a luminous region which emits light in the luminance corresponding to a voltage between the above described first and second electrodes and its thickness, the above-mentioned luminescent layer which has the thickness of differing in a layer thickness direction so that the luminance of the luminous region may become uniform (for example, see Japanese Patent Laid-Open No. 11-40362 publication). The above-mentioned first electrode has a first terminal for applying a voltage, and the second electrode is provided with facing the first electrode, has a second terminal for applying a voltage, and exhibits a sheet resistance lower than that of the above mentioned first electrode.